1. Field of the Invention
The present invention relates to a hand position detecting device which detects the rotational positions of seconds, center and hour hands, for example, of a timepiece and electronic apparatus including the detecting device.
2. Description of the Related Art
In the past, a hand position detecting device which detects the rotational positions of hands of a timepiece is known, as disclosed by Japanese Published Unexamined Application 2000-162336. This device comprises a first drive system in which a first drive motor transmits its rotation to a seconds (hand) wheels which in turn causes a seconds hand to sweep around a dial, a second drive system in which a second drive motor transmits its rotation to seconds and hour wheels to cause the seconds and hour hands, respectively, to sweep around the dial. This device also includes a detector which when the seconds, center and hour wheels of the first and second drive systems are rotated on the same axis, optically detects, with the aid of a light emission element and a photodetection element included in the detector, a first, a second and a third light-passing aperture provided in the seconds, center and hour wheels, respectively, such that the respective rotational positions of the seconds, center and hour wheels and hence the seconds, center and hour hands are determined based on detected signals from the detector.
In this case, the first driving system comprises a fifth wheel with three light-passing apertures provided at angular intervals of 120 degrees for transmitting rotation of the first driving motor to the seconds wheel. This seconds wheel has eleven light-passing apertures provided at angular intervals of 30 degrees along the periphery thereof and a light blocking area provided between the first and last apertures along the periphery of the seconds wheel. Thus, when in the first driving system the fifth wheel rotates and one light-passing aperture aligns with a detection unit, the seconds wheel also rotates. Then, when its light blocking area blocks a light-passing aperture in the fifth wheel and then a first one of the apertures in the seconds wheel aligns with a light-passing aperture in the fifth wheel, thereby causing the detection unit to detect light, the seconds hand indicates a time o'clock.
An alternative to the seconds wheel has a pair of arcuate openings of predetermined lengths formed along the circumference thereof on opposite sides of a light blocking area provided at a reference position in the second wheel. The seconds wheel also has a light-passing aperture provided between the distal ends of the pair of arcuate openings in the seconds wheel from the light blocking area so as to be on the same diameter of the seconds wheel as the light blocking area. In this case, the arrangement is such that when in the first driving system the fifth wheel rotates so that one of its light-passing apertures aligns with the detection unit, the seconds wheel also rotates; its light blocking area blocks a relevant light-passing aperture in the fifth wheel; and then a part of one of the pair of arcuate openings in the second wheel following the light blocking area of the seconds wheel aligns with the light-passing opening in the fifth wheel, thereby causing the detection unit to try to detect light. When the detection unit detects light at this time, the seconds hand points to a time o'clock.
In the former first driving system employing the first-mentioned seconds wheel, when one of the three light-passing apertures provided at 120 degrees in the fifth wheel aligns with the detection unit, the rotational position of the seconds wheel is required to be detected. Thus, when the fifth and seconds wheels are assembled, both are required to be positioned accurately relative to each other, which render the assembling work complicated.
In this first driving system, a total amount of light is small which passes through the eleven light-passing apertures provided at the angular intervals of 30 degrees along the periphery of the seconds wheel. Thus, when the seconds wheel is rotated at high speeds to detect the rotational position thereof, there is a possibility that all the eleven apertures cannot be detected securely and hence the position detecting speed is limited.
In the latter first driving system employing the alternative seconds wheel, this seconds wheel has the light-passing aperture provided at the reference position in the seconds wheel and the pair of arcuate openings provided on opposite sides of the light-passing aperture. Thus, the quantity of light passing through the pair of openings is large and the rotational position of the seconds wheel can be detected at high speeds. When the light-passing aperture in the fifth wheel aligns with the detector and part of the other of the pair of openings following the light blocking area in the seconds wheel aligns with the detection position, thereby causing the detection unit to detect light, the seconds hand points to a time o'clock. Thus, even when the detection unit aligns with any point in the other opening, it is determined that the seconds hand points to a correct time o'clock. Thus, the rotational position of the seconds wheel cannot be located accurately.